Field of the Invention
The present invention relates to a vehicle wheel axle assembly, particularly including aspects that facilitate the connection between axle of a vehicle wheel and the frame to which the vehicle wheel is mounted. More specifically, the present invention relates to a vehicle wheel axle assembly with a threadable connection to the frame that includes a multiple-lead thread engagement. The present invention is particularly applicable to a bicycle wheel axle assembly that facilitates the connection between axle of a bicycle wheel and the frame of a bicycle.
Discussion of Prior Art
Heretofore, the prior art threadable axle assemblies for bicycles and similar vehicles (commonly referred to as “through-axles”) employ common single-lead thread engagement between the axle and/or the control shaft to threadably secure the wheel axle to the bicycle frame and/or fork.
It is highly desirable to be able to install and uninstall the bicycle wheel to the frame very quickly and easily. Particularly in bicycle racing conditions, when every second counts, the ability to quickly swap out wheels (in the case of a flat tire, for instance) is critical. Reducing the time required to install and uninstall the wheel may result in the margin of difference between winning and losing the race.
This single lead thread engagement utilizes a thread with only a single thread start. The axle and/or control shaft commonly employs an external (male) thread, while the frame commonly employs a mating internal (female) thread to achieve a threadable engagement therebetween. When the external thread of the axle and/or control shaft is presented to the internal thread of the frame, there is only a single point of initiation (start) of initial engagement that is possible within 360 degrees of rotation. As such, the operator will need to rotate the axle and/or control shaft by up to 360 degrees (i.e. a full revolution) before the axle and/or control shaft initiates the threadable engagement. This full revolution of the axle and/or control shaft results in time-consuming lost motion when installing or uninstalling the wheel to the frame.
Once the operator has initiated this threadable engagement, he/she must next rotate the axle and/or control shaft to advance this threadable engagement to axially overlap the external thread relative to the internal thread to the point where the wheel is secured to the frame. Upon securing the wheel to the frame, it is desirable to have achieved a certain minimum axial thread engagement to insure the alignment and strength of this threadable engagement. This minimum thread engagement is related to several factors as is well known in industry. With a conventional single-lead thread engagement, the axial thread engagement advances by a single thread pitch with each rotation of the axle and/or control shaft. The result is a relatively “slow” threadable advancement, with a corresponding large number of manual “turns” or revolutions of the axle and/or control shaft required for a given axial advancement of the threadable engagement. This large number of revolutions is time-consuming and further adds to the time and motion required to install and/or uninstall the wheel to the frame.
One potential method to increase the “speed” of the threadable engagement and reduce the number of revolutions of the axle and/or control shaft for a given axial advancement of the threadable engagement is to increase the pitch of this single-lead thread. However, an increased pitch commonly corresponds to a thread profile of greater radial depth. This greater thread depth requires the removal a greater amount of material in both the axle and/or control shaft and the mating component of the frame, thus further weakening these elements. While other coarse thread forms may exist, such as the acme thread form, these thread forms are very expensive to produce in comparison with conventional vee-shaped thread forms.
Another potential method to increase the “speed” of the threadable engagement and reduce the number of revolutions of the axle and/or control shaft for a given axial advancement of the threadable engagement is to employ a bayonet-type thread system or a “quarter-turn” rotational fastening system, such as fastener arrangements popularized by Dzus®. Such fasteners utilize a circumferential cam-and-follower engagement where a portion of the cam surface may have a helical ramping geometry that may resemble a helical thread. However, such fasteners have limited range of circumferential or rotary engagement that is less than 360 degrees, hence they are common termed as “quarter turn” fasteners. This is in contrast to conventional thread systems that utilize the threadable engagement of continuous helical thread flanks that commonly engage through at least a full revolution, and most commonly several revolutions. Due to their limited range of circumferential engagement, quarter-turn fasteners also have very limited axial engagement. Further, since their axial range of engagement is commonly axially predetermined and fixed, the axial stack-up tolerances of the fastened components must be held very closely, with tight tolerances that add to cost. Still further, in contrast to conventional helical threads, this cam-and-follower engagement has very limited surface area of contact and severely limited circumferential overlap angle of engagement, which results in high contact stresses and further restricts the axial load bearing capacity of this engagement and the smoothness of the rotational actuation. This circumferential overlap angle of engagement is commonly less than 90 degrees. Due to their significant limitations, such quarter-turn fasteners are commonly employed merely as a key to position and/or retain two components to each other, rather than to threadably clamp and positively secure two components to each other or to provide a structural connection.
Another shortcoming of conventional single-lead threads is that, depending on the pitch of the thread and on the ability to maintain perfect alignment between the axle and/or control shaft relative to the frame, a single-lead thread will have a relatively high propensity for cross-threading during initiation of the threadable engagement. As is well-known in industry, such cross-threading can easily deform and damage the thread form and make it difficult or impossible to later thread these two parts together.